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Re: Simulator: base_insn and insn in decode.c
I switched to the SID framework. I found it easier to create a new
target. The disassemby works better as it calls this disassembler code
in src/opcodes. But I'm still in trouble with decode.cxx. It looks the
same as in sim. I'n my opinion the entire_insn should alwasy be left
aligned and not right_aligned as it is now. Base_insn should have the
same alignment. I think this way it is easier to support variable sized
instructions.
Best Regards
Ronald
Dave Brolley wrote:
I forgot to address your other question which was about the difficulty
of setting entire_insn before decoding. It's a bit of a chicken and
egg situation isnt'y it? You can't set entire insn properly until you
know something about the insn, but you can't call decode without
setting entire_insn properly.
Your method of calling decode twice won't work because of this.
Most existing ports determine the insn length by looking at a few bits
in base_insn and use this information to fill entire_insn.
I'm wondering if the decoder shouldn't be redesigned so that all it
takes is base_insn, which should be all that is necessary to identify
the insn. The extractors for each format would then read any
additional bytes as needed. There is already support for this for ISAs
with insns which are longer than an insn word.
Dave